A typical refrigeration system comprises at least one evaporator contained within the space that is to be cooled, a condenser that is located outside of the cooled space, a compressor positioned between the evaporator outlet and the condenser inlet, and an expansion valve. A refrigerant circulating through the system is compressed by the compressor which raises the temperature and pressure of the refrigerant. The then hot pressurized refrigerant gas flows through the condenser which serves as heat exchanger to allow the refrigerant to dissipate heat. The refrigerant condenses into a liquid and then flows through the expansion valve, where the liquid refrigerant moves from a high pressure zone into a low pressure zone, thus expanding and evaporating, and thereby becoming cold. The cold refrigerant passes into coils of the evaporator, thus absorbing heat from inside the space that is to be cooled. The evaporator could be located, for example, in the plenum of a forced air residential or commercial air conditioning system through which air is blown for cooling the interior of the residence or building. Other applications include automotive air conditioning systems and commercial food storage units.
A commonly used expansion valve for controlling flow of the compressed and liquified refrigerant from the condenser to the evaporator is a thermostatic expansion valve (TEV). Thermostatic expansion valves have employed a liquid-filled capsule sensing the temperature of the refrigerant discharging from the evaporator. Expansion of the fluid in the chamber operates a pressure responsive moveable valve member for controlling the liquid refrigerant flow through the valve. Such diaphragm actuated thermal expansion valves are often used in automotive air conditioning systems for controlling refrigerant flow where rapid changes in operating conditions require a high degree of responsiveness by the valve.
Many if not all conventional thermostatic expansion valves cannot meet the higher efficiency standards (SEER seasonal efficiency ratio) being set by law in some jurisdictions, such as the United States. In addition, manufacturers needed to stock a large number of different valves for use with different sizes and refrigerant types. Another drawback is the mounting of the valve components, in particular the pressure sensing tubes and temperature sensing bulb, can be cumbersome. Also, additional test equipment and job site visits often is necessary for troubleshooting the valves.
Several types of electrically actuated expansion valves also are known. One type includes a solenoid connected to an appropriate electrical supply which, in response to a pulsed electrical signal, actuates a plunger or control element alternately into and out of a flow path through an expansion valve body to permit or prevent fluid flow. Another type of electrically actuated expansion valve has a rotary actuator with a mechanism for converting the rotary motion into linear motion for operating a valve element to increase or decrease the flow area available through the valve body by seating against the valve seat to close the valve and prevent flow, or, moving linearly away from the valve seat, to permit flow through an area defined by the area of the opening between the valve element and the valve seat.
While electrically actuated valves overcome some of the drawbacks associated with thermostatic expansion valves, problems still exist. For instance, current electronic systems require the valve, sensors and electronics to be hard-wired and individually installed at the installation site.